1. Field of the Invention
The present invention relates in general to a fluid-filled elastic mount adapted to provide a vibration damping effect on the basis of flows of a fluid, and more particularly to such a fluid-filled elastic mount wherein a resonance member which is oscillated upon application of a vibrational load to the mount partially defines a restricted fluid passage.
2. Discussion of the Related Art
There is known an elastic mount such as an engine mount for a motor vehicle, which is interposed between two members of a vibration system such that those two members are flexibly connected to each other, or such that one of the two members is supported by the other member in a vibration damping or isolating manner. One example of such an elastic mount is a fluid-filled elastic mount wherein a first and a second mounting member which are attached to the respective two members of the vibration system are spaced apart from each other and elastically connected by an elastic body, which partially define a fluid chamber filled with a non-compressible fluid, so that a vibrational load applied to the elastic mount is damped on the basis of flows or resonance of the non-compressible fluid. One type of such a fluid-filled elastic mount is disclosed in JP-U-2-31933, wherein a hat-shaped resonance member supported by the first mounting member is disposed in the fluid chamber partially defined by the elastic body, such that the fluid chamber is substantially divided by the resonance member into two sections on the opposite sides of the resonance member as viewed in a direction (hereinafter referred to as "load-receiving direction") in which the vibrational load is primarily applied, and such that the periphery of the resonance member cooperates with the corresponding portion of the inner surface of the fluid chamber to define an annular restricted fluid passage which permits restricted flows of the fluid between the two sections of the fluid chamber. The restricted fluid passage partially defined by the hat-shaped resonance member can be adapted to have a comparatively large area for fluid communication, and is effective to damp the vibrations whose frequencies are medium or relatively high. The resonance member may be positioned so that its peripheral portion is opposed to and abuttable on a stop portion provided on the second mounting member, for limiting the amount of relative displacement of the first and second mounting members in the load-receiving direction.
In the fluid-filled elastic mount constructed as described above, the frequencies of the vibrations that can be damped on the basis of resonance of the fluid flowing through the annular restricted fluid passage can be adjusted by tuning the area of the annular restricted fluid passage. To this end, the size of the resonance member is suitably determined so as to establish the desired width of the annulus of the restricted fluid passage, that is, the distance between the maximum or largest outside diameter of the resonance member and the inner surface of the fluid chamber, depending upon the desired damping characteristics to be exhibited by the elastic mount. Where the fluid-filled elastic mount is used as a motor vehicle engine mount, the annular restricted fluid passage may be tuned to effectively damp high-frequency vibrations such as a gear noise, and a booming noise generated during running of the vehicle at a relatively high speed. In this case, the restricted fluid passage should have a relatively large area or width, and the resonance member should have an accordingly small size (accordingly small maximum outside diameter).
However, a decrease in the size of the hat-shaped resonance member results in a decrease in the area of contact of the resonance member with the stop portion indicated above. Hence, it has been difficult to enable the elastic mount to exhibit the desired damping characteristics with respect to the high-frequency vibrations, while assuring an excellent function of limiting the relative displacement of the first and second mounting members by the abutting contact of the resonance member with the stop portion.
JP-A-60-104824 discloses a fluid-filled elastic mount wherein a disk-like resonance member attached to the first mounting member and partially defining an annular restricted passage has through-holes formed through its thickness, so that the through-holes act as secondary fluid passage and cooperate with the annular fluid passage to provide restricted fluid passage means having a relatively large total area for fluid communication. The publication identified above also discloses a disk-like resonance member having radial slots in place of the through-hole. However, the fluid-filled elastic mount wherein the resonance member has such through-holes or radial slots is still unsatisfactory in the fluid communication area of the restricted fluid passage means. In other words, the disk-like resonance member formed with through-holes or radial slots having a sufficiently large total fluid communication area inevitably suffers from a considerable amount of reduction in its strength and a high possibility of deformation thereof upon abutting contact with the stop portion, leading to a failure of the resonance member to function as stop means in cooperation with the stop portion.